1. Field of the Invention
This invention relates to an electrochemical method for the selective production of partially oxidized organic compounds such as alcohols, aldehydes, acids, and the like, at the catalytic anode of a fuel cell. Oxide anions are formed at the fuel cell cathode by ionization of oxygen-containing gas, and transported through electrolyte to the fuel cell anode where selective partial oxidation of organic compounds is facilitated by the fuel cell anode which comprises, at least in part, a catalyst selected from elements of the Periodic Table appearing in a group selected from the group consisting of Groups IB, IIB, IIIA, VB, VIB, VIIB and VIII. One important application of this invention relates to the production of methanol by partial oxidation of hydrocarbon gases, particularly natural gas, at the catalytic anode of a fuel cell.
2. Description of the Prior Art
Substantially all the methanol synthesized currently is produced by the catalytic hydrogenation of carbon monoxide. Carbon monoxide is supplied as synthesis gas comprising carbon monoxide and molecular hydrogen which is generally obtained by steam reforming of a hydrocarbon such as methane. Thus, two separate chemical reactions, requiring different reaction conditions, separated reaction zones or vessels, transport of product and reactants are performed in the conventional methanol synthesis processes, which operate at temperatures of about 250.degree. to about 350.degree. C. and at pressures of about 700 to 1500 psi. Because sufficiently active catalysts are not available to conduct the methanol forming reaction at preferred lower temperatures and pressures, higher than ideal temperatures and pressures are required to enhance the thermodynamically limited yield of methanol. The development of more active catalysts has lowered the temperature and pressure requirements during the formation of methanol from synthesis gas, but costs associated with reactor temperature control, compression and recirculation remain high.
Alternative methanol synthesis processes have focused on direct catalytic partial oxidation of methane, but direct partial oxidation processes have not been generally successful because suitable catalysts and reactors for controlling the oxidation have not been developed. Operating conditions of temperature and pressure, the condition of the reactor vessel surface and the catalyst "state" influence reaction kinetics, product yield and product composition. Methane synthesis by direct partial oxidation must be very closely controlled to maximize specificity and to minimize the formation of higher oxidation products.
A fuel cell system (hydrogen/chlorine) having a hydrogen diffusion anode, a halogen diffusion cathode, and utilizing molten halide or hydrogen ion containing electrolyte is taught in U.S. Pat. No. 3,669,750. One modification of this system is adapted for in situ reforming of fuels in molten alkali carbonate cells, and partial oxidation of the hydrocarbon fuels to alcohols, aldehydes, and is combined with direct reforming of these products. Hydrogen used as fuel, or produced during the reforming reaction, is the electrochemically active fuel. Water must be present, in the form of steam, to conduct reforming with a nickel catalyst to carbon dioxide and hydrogen. Any partial oxidation of hydrocarbons to alcohols, aldehydes, and the like, which occurs in this fuel cell is only incidental to the direct reforming reaction.
A fuel cell system in which internal reforming of the hydrocarbon content of fuel cell supply gas is achieved is described in U.S. Pat. No. 4,365,007. The hydrocarbon content of fuel supply gas, including methane, is reformed to produce hydrogen and carbon monoxide in molten carbonate and phosphoric acid fuel cells to provide electrochemically active components which can participate in the fuel cell reaction, and to offset heat generated in the cell during operation. Another method of reforming fuel to hydrogen in situ in electrochemical cells, is taught by U.S. Pat. No. 3,407,094. Partial oxidation is again mentioned as an incidental electrochemical reaction, but the principal and desired reaction is the reforming of fuel to hydrogen in a hydrogen anode system. U.S. Pat. No. 3,585,077 discloses an apparatus for controlling the fuel feed to a fuel cell system in which a reformer is separate from the fuel cell itself. Preparation of polyamides by electrolytic polymerization of lactams is taught by U.S. Pat. No. 3,419,482. A pressurized, high temperature fuel cell power plant is described in U.S. Pat. No. 4,041,210.
Oxidation of ethylene to ethylene oxide in the presence of a silver or silver alloy catalyst on a support such as alumina, in a plurality of electrolytic cells having solid electrolyte capable of transporting oxygen ions, is taught by U.S. Pat. No. 4,329,208. Trace amounts of chlorinated hydrocarbons may be added to the gas phase to increase the selectivity of the reaction to ethylene oxide upon application of voltage between two catalysts through a solid electrolyte.
Oxidation of ammonia to nitric oxide using porous platinum films deposited on an yttria-stabilized zirconia solid electrolyte fuel cell is described in "Cogeneration of Electric Power and Nitric Oxide in a Solid-Electrolyte Fuel Cell", M. R. S. Manton et al, 11th Energy Technology Conference, 1984.